This invention relates to an instant synchronous automatic gain control apparatus and particularly an automatic gain control apparatus for barcode reading devices.
The design of automatic gain control (AGC) circuits used in conventional barcode reading devices mostly employs the feedback control gain type. When detecting that output signal power is not adequate, it uses a feedback method to amplify the gain of the preceding stage for boosting the following signal. This method uses average value to control gain value and does not have a synchronization problem. It is easier to control and especially suitable for the environments where maintaining signal amplitude variation proportion is desired. However if the requirements are to get frequency without influencing by the circuit and to get output signals with same level, the design set forth cannot meet all the needs. Because for reaching the condition of every output has the same phase, every signal has to make synchronous gain adjustment. Using the feedback approach to adjust amplification gain, when the gain is adjusted for a preceding stage based on the detected signal, the signal has already passed the amplifier. Hence the produced result of the changing gain affects only the next set of signals. If the average value is not used, it could happen that the next signal might be too strong and result in over saturation or signal distortion. As aforesaid AGC design cannot perform instant synchronous control for adjusting gain, it cannot rectify amplification gain for every signal individually. By taking the average value, it is not an instant synchronous amplification gain adjustment.
It is therefore an object of this invention to resolve aforesaid disadvantages by providing an instant synchronous automatic gain control apparatus that is capable of performing instant signal and gain control process synchronously when the signal received by the barcode reading device is weak.
The instant synchronous automatic gain control apparatus according to this invention includes a sensor unit, a current amplification unit, a first stage amplification unit, a buffer stage amplification unit, a signal pickup amplification unit, a second stage amplification unit, a third stage amplification unit, a signal output amplification unit, a signal isolation match unit, and a signal rectification unit. When the barcode reading device receives a weak signal, the apparatus of this invention may process the signal and gain control synchronously and transmits desired digital signals to a microprocessor (CPU) or decoder circuit for process.